Lead-poisoned birds may have saved human lives.

Dec 01, 2008

Gulson B, M Korsch, M Matisons, C Douglas, L Gillam and V McLaughlin. 2008. Re-entrained lead carbonate as the main source of lead in blood of children from a seaside community: an example of local birds as “canaries” in the mine. Environmental Health Perspectives doi: 10.1289/ehp.11577.

Synopsis by Heather Hamlin

A modern day 'canary in a coal mine' unfolds as thousands of birds “dropping from the sky” alert authorities to lead-tainted drinking water and people.

Residents of a seaside community in Australia had unusually high concentrations of a unique and toxic form of lead that was discovered after thousands of local birds died.

Scientists who were called in to examine the birds found lethal lead levels in the animals. They traced the contamination to the extensive transport of mined lead by road and railroads to a local shipping port. The lead hauling had begun less than two years earlier yet had contaminated water, soil, animals and residents living nearby.

Different forms of lead, called isotopes, are present in the environment. Lead carbonate - the type found in the nearby mine - has a unique isotope signature that easily distinguishes it from other types of lead, such as the kinds found in paint, solder and petrol products.

The deaths of the birds from lead toxicity was especially concerning given that it was lead carbonate that likely killed them. Lead carbonate is more toxic than other forms of lead. This dangerous variety easily penetrates lung tissue and is highly absorbed by blood.

The people were probably contaminated through eating and breathing the lead carbonate dust. Researchers measured blood lead levels in 49 children younger than 6 years old and found from 30 to 93% of the lead in their blood was the more toxic variety. Blood lead levels in the children ranged from 1.5 to 25.7 micrograms per deciliter. Adults had a wider mix of different types of lead.

In the US, the Centers for Disease Control considers blood lead levels lower than 10 micrograms/deciliter safe, although some researchers believe there is no safe level for children.

Researchers found lead carbonate in local drinking water supplies and in the residents themselves. The affects of lead toxicity are well known, and include neurological, cardiovascular and reproductive damage. Had it not been for the birds acting as the “canaries in the coal mine” the presence of the lead may not have been discovered, leading to a potentially tragic outcome for the community.